Analysis of PAN and PEGDA Coated Membranes for Filtering Water with Reduced Fouling and Increased Heavy Metal Adsorption

An increase in United States water pollution has been denoted over the past 30 years. With a rise in water pollution, enhanced filtration and heavy metal remediation methods are imperative. Membrane fouling, the process whereby extraneous particles deposit onto a membrane surface and degrade the membrane’s performance, is a major issue facing ultrafiltration. This study’s goals were to enhance membrane flux and anti-fouling performance with a PEGDA filter and to compare the efficiency of PVAm and PEI for heavy metal adsorption. Electrospinning was employed to create membrane platforms for coating and grafting polyethylene glycol diacrylate (PEGDA), N,N’Methylenebisacrylamide (MBAA), cellulose nanofibers (CNF), polyvinyl alcohol (PVAm) and polyethylenimine (PEI). The anti-fouling performance of electrospun PAN membranes was determined by coating the surface with CNF, PEGDA, and MBAA, which were chosen due to their hydrophilic and low-fouling properties. Coating the top layer of the membrane with these hydrophilic polymers achieved a flux that remained constant at the quickest rate, at least 20% quicker than that of polyethersulfone (PES) commercial filters. The membrane containing .02% CNF and 0.2% PEGDA exhibited 90% rejection and 99% recovery, indicating that CNF and PEGDA exhibited better fouling resistance than PES. The high fouling performance of the commercial membranes can be attributed to the highly hydrophobic nature of PES, making it prone to membrane fouling. In order to evaluate heavy metal adsorption membrane performance, electrospun PAN membranes were immersed in concentrations of H2SO4 (50-70 wt%) to introduce negative charges creating bonds between PVAm, PEI, and the PAN membrane. The outcomes of static adsorption tests indicated that PVAm adsorbed heavy metals at a rate that was ~8-30 mg/g greater than PEI. The higher adsorption rate can be attributed to the increased surface area resulting from the grafted PVAm. In the future, a combined PEGDA, PAN, and polyvinyl chloride (PVC) membrane should be designed to adsorb heavy metals while reducing fouling. The efficacy of modified periods of extensive filtration should also be evaluated. Introduction Although the world population is 6.8 billion, 1.2 billion people do not have clean drinking water access1. It is estimated that onethird of the population will face severe water shortages by 20252. As the world population increases by 80 million annually, water shortages also threaten to reduce the global food supply3. Most Analysis of PAN and PEGDA Coated Membranes for Filtering Water with Reduced Fouling and Increased Heavy Metal Adsorption Kristin Wong1,3*^, Brendan Liu1,3*, Serena McCalla2, Benjamin Chu4, and Benjamin Hsiao4 Student1, Teacher2: Jericho High School, 99 Cedar Swamp Road, Jericho, NY 11753 Intern3, Mentor/Professors of Chemistry4: Stony Brook University, Stony Brook,New York 11794 *These authors contributed equally ^Correspondence: [email protected] desalination plants currently rely on flash evaporation, distillation, and electrodialysis for the removal of contaminants, like salt, from water. However, widespread applications are limited by high-energy costs in many third world countries4. In parallel, high levels of heavy metal pollution have been detected in various water resources throughout the world5. Over 80% of wastewater in developing countries is discharged without treatment, contaminating coastal areas, rivers, and lakes6. With the alarming increase in industrialization and urbanization, the consumption of Chromium (VI) water has been categorized as a major dilemma across the United States7. Imbibition of this heavy metal causes detrimental and permanent health damage due to its carcinogenic effects. Apart from lung cancer and death, the most common effects of ingestion of Chromium (VI) on humans are respiratory problems, genetic alteration, kidney and liver damage, and weakened immune systems8. Current day filtration techniques include reverse osmosis, hydroxide precipitation, ion exchange, and solvent evaporation. However, many of these methods require large quantities of time and energy, yet produce miniscule filtration and adsorption capabilities. Electrospinning, a process that uses an electrical current to draw very fine fibers from a liquid, reduces fabrication time for membranes, while introducing small pore sizes for efficient filtration. The use of electrospinning in creating the fibrous membranes allows for random, yet minute pore sizes to be established onto the substrate9. Introducing small pore sizes on the surface of the membrane increases surface area for enhanced heavy metal ions adsorption. Polymer grafting produces one or more types of polymer blocks and chains connected to a primary chain of a macromolecule10. The introduction of sulfuric acid etches negative charges on the surface of the membrane for polymer grafting11. These negative charges are complemented by the positively charged polymers, which will present active sites that attract the heavy metal ions onto the membrane surface12. The use of thin film composite (TFC) membranes, which typically consist of 2-3 thin layers, is a robust and efficient method of purifying water13. Yung et al. (2010) demonstrated a novel type of TFCs, called thin film nanocomposite (TFNC) membranes. The bottom layer of this three-tier membrane is a tough, non-woven fibrous material, polyethylene terephthalate (PET). The mid-layer, which supports the barrier layer, consists of electrospun polyacrylonitrile (PAN) fibers, which are typically used for the fabrication of microfiltration (MF) and ultrafiltration (UF) membranes14. The top coating layer, which serves as the barrier between solutes and permeates, is constructed with ultra44 January 2012 Volume 1 Issue 3 Kristin Wong, Brendan Liu, Serena McCalla, Benjamin Chu, and Benjamin Hsiao Page 2 of 7 45 fine cellulose nanofibers (CNF)(Figure 1). PAN (Polyacrylonitrile) has good mechanical properties, good chemical resistance, and is costefficient. However, during filtration of wastewater, its hydrophobic nature can dramatically decrease the water permeability due to the tendency of biomacromolecule fouling. The use of cellulose nanofibers in creating membranes increases surfaceto-volume ratio to achieve high flux, high durability and high retention with minimal environmental impact. The hydrophilicity of cellulose, due to its large number of hydroxyl groups, gives cellulose nanofibers their anti-fouling characteristic13. Membrane fouling is a significant problem facing ultrafiltration (UF). Permeate flux substantially and irreversibly decreases due to the growth of biofilms on the membrane surfaces, causing a blockage in its pores15. Applying a hydrophilic surface coating layer to UF membranes is a potential method of improving their resistance to fouling and maximizing their lifespan13. Polyethylene glycol (PEG)-based materials have been considered for several coating applications due to their excellent resistance to fouling and macromolecule adhesion, amphiphilic nature, and biocompatibility15. By varying the concentration or molecular weight of polyethylene glycol diacrylate (PEGDA), its material properties, including mesh size, bioactivity, and degradation rate, can be tightly regulated and systematically modified16. N,N′-Methylenebisacrylamide (MBAA) has a hydrophilic nature as well as the ability to serve as a crosslinking agent, therefore synthesizing membranes during freeradical polymerization while increasing filtration performance17. Essentially, hydrophilicity refers to the hydrogen bonding that occurs between polar water molecules. Membranes coated with hydrophilic polymers like MBAA have nitrogen or oxygen in their backbone structure. Therefore, they contain polar functional groups that bond with molecules of water, reducing the buildup of biofilms on membrane surfaces and improving the membrane’s ability to adhere to liquid18. Filtration membranes undergo major pressure differentials, so creating a top coating that is as thin as possible is crucial. A thin top coating would have the ability to withstand the shear force and pressure exerted by the fluid in cross-flow filtration19. Due to its solvent-free formulations, high polymerization rate, low energy consumption, ambient temperature operation, and ability to tailor polymer properties, UV crosslinking polymerization is widely used to create barrier layers on filtration membranes20. The crosslinking molecules absorb the photons energy via electronic excitation when exposed to UV light. This selective excitation is used to initiate synthesizing chemical reactions by generating reactive species (free radicals or ions)21. By using the UV crosslinking process (Figure 2), the creation of a dense and tight coating layer for cellulose nanofibrous membranes could be achieved. A major goal of this study was to evaluate the anti-fouling properties of thin film nanocomposite membranes synthesized via UV crosslinking. By integrating the cellulose barrier layer Figure 1. Artistic representation of PET support, PAN mid-layer and cellulose coating. Photoinitiator: UV radiation reactive species: multifunctional monomer cross-linked polymer Figure 2. UV crosslinking process (adapted from Decker et al.10) with hydrophilic UV-sensitive polymers like PEGDA and MBAA, a novel dense barrier layer that can increase membrane specificity and minimize foulant contact with underlying support layers (without severely compromising membrane flux) can be synthesized. This study’s goal was also to determine the characterization of the electrospun nanofibers of 8 wt% PAN for heavy metal adsorption. By grafting modified PAN electrospun nanofibers with polyethyleneimine (PEI) and polyvinyl alcohol (PVAm) onto an electrospun membrane, enhanced heavy metal adsorption rates would be achieved. Materials and Methods Cellulose Nanofiber Membrane Preparation: The electrospinning process was used to create the mid-layer PAN nanofibrous scaffold, which was then placed on top of the PET non-woven substrate. The combined PET substrate and PAN scaffold were soaked in hydrochloric (HCl) acidic water (pH = 2) for 1 minute. A 7.62 by 10.16 cm membrane was cut, and its edges were taped to a glass plate. A rubber roller was used to drain the excess water. Roughly 4.0 g of a cellulose nanofiber aqueous suspension (.05 wt%) was cast onto the PAN/PET support and was evenly dispersed over the membrane with the barrier layer thickness regulated by the layers of tape. A cellulose gel was formed immediately upon contact at the interface between the water and cellulose solution. The cellulose nanofiber was thoroughly washed with water and then dried at 100 ̊C for 20 minutes after coating. Coating the Cellulose Nanofiber/PEGDA/MBAA Barrier Layer: PEGDA with January 2012 Volume 1 Issue 3 Kristin Wong, Brendan Liu, Serena McCalla, Benjamin Chu, and Benjamin Hsiao Page 3 of 7 46 a typical Mn of 258 and PEGDA with a typical Mn of 575 (Sigma Aldrich) were dissolved in acetone and the crosslinking photo-initiator, MBAA (Sigma Aldrich), was added to each solution at approximately 5% of the total solute mass. The prepared solutions were coated onto the cellulose barrier layer of the cellulose-based UF membranes. In order to form a single coating, 4.0 g of a cellulose nanofiber and polymer suspension was cast onto the PAN scaffold/PET substrate. Table 1 details all prepared solutions and their respective parameters. The network formation was achieved via UV-initiated free-radical photopolymerization under UV wavelength of 365 nm using an ELC 500 (Electro-Lite, Corp) UV-crosslinking machine. Commercial Membranes: Koch HFK 328 (Koch Membrane), Pall 3K (Pall Life Science), and Pall 5K (Pall Life Science) were the commercial membranes used for comparison with our modified membrane. The Koch HFK 328 membrane is composed of proprietary semi-permeable polyethersulfone (PES). The Pall membranes are made of low protein-binding modified PES. The hydrophobicity of PES often limits its application because hydrophobic membrane surfaces foul rapidly and result in the reduction of permeation rate22. Cellulose Nanofiber Membrane Characterization Flux Determination: A Millipore stirred (dead-end) cell (model 8050) with an effective filtration area of 0.00134m2 was used in order to evaluate the flux and rejection ratio of each membrane sample. The membrane samples that were placed within the dead-end cell were cut into 40 mm diameter circles. A water permeability test was then carried out. The water flux was measured every 5 minutes at 30 psi. A graduated cylinder was used to measure the amount of permeate. Rejection Ratio Determination: The rejection percentage (R%) was used to evaluate the filtration performance of the membranes. The rejection percentage was determined by Equation 1. In order to equilibrate the surface hydrophobicity of the membrane, 50 mL of pure water permeate was collected. Following this equilibration, 50 mL of a 1000 ppm polyethylene glycol (PEG) (Sigma Aldrich) aqueous feed solution was used to test the rejection efficiency. PEG solutions with molecular weights of 4600 kDa and 10000 kDa were prepared. Filtration was carried out at room temperature and the operating pressure was 30-40 psi. A total organic carbon analyzer (TOC-V, Shimadzu Corp.) was employed to determine the molecular weight cut-off (MWCO) of the membranes. The MWCO method was used to infer the membrane pore size based upon the molecular weights of a particular molecule that the membrane was capable of rejecting. By determining the organic carbon concentration of the permeate and feed solutions, the TOC-V can be used to calculate the rejection percentage using Equation 1. Anti-Fouling Properties and Flux Recovery: An anti-fouling test was carried out in order to determine the anti-fouling properties of each membrane. Multiple trials to determine a constant water flux were carried out. The water flux was recorded every 5 minutes at 30 psi until it remained the same for 15 minutes, the result of multiple trials that determined a constant water flux. After the water flux became constant, protein feed solution was prepared by dissolving Bovine Serum Albumin (BSA) (Sigma Aldrich) in 0.01M phosphate buffered saline (PBS) (pH=7.4) to produce 1 g/L BSA solution, 50 mL of which was then poured into the dead-end cell. BSA was deployed due to its ability to adhere to the membrane surface, providing a clear indication of the membrane’s anti-fouling performance. In order to stabilize the charges of the protein, PBS was incorporated in the BSA solution. The protein flux was recorded every 5 minutes at 30 psi until steady. After the BSA flux was recorded, the membrane was flushed with DI (deionized) water. In order to determine the recovery ratio of the membrane, the water flux before and after the flushing of the membrane were compared. The flux recovery ratio was determined by Equation 2. Water Contact Angle Measurement: A droplet of water was placed onto each membrane cutout. An optical contact angle meter (CAM200, KSV Instruments, LTD) was used to determine the surface hydrophilicity formed by the water droplet and the thin film coating layer on the membrane surface. Membrane Preparation for Heavy Metal Adsorption Polyacrylonitrile (PAN) solution of 8 wt % was prepared by dissolving and stirring of PAN powder into N, N-Dimethylformamide (DMF) at 60°C overnight. The solution was cooled to room temperature before use. Electrospinning conditions were as follows: 1) solution feeding rate was set to 20 ul/min., 2) applied voltage to 16 kV, and 3) spinneret-to-collector of a distance of 9 cm. The electrospun nanofibers were deposited onto non-woven polyethylene terephthalate (PET) substrate. A stepping motor was used to control the oscillatory translational motion. That motion was perpendicular to the drum rotation direction which ensured a uniform electrospun membrane with sufficient membrane area. The thickness of membranes was controlled at 30 um by adjusting the delivered volume of the polymer solution. To introduce negative charge onto the nanofibers, the electrospun membrane was immersed into 50, 60, and 70 wt% concentrated sulfuric acid and kept for 15 min. at room temperature. The membrane was then immersed in water several times to Equation 1. Cfeed and Cpermeate are the concentrations of the feed solution and permeate solution. Recovery % = (Jw1/Jw2 ) X 100% Equation 2. Flux recovery ratio. Jw1 is the steady pure water flux before the BSA test and Jw2 is the steady pure water flux after the BSA test. Table 1. Membrane Coating Solution parameters for PAN/PET support. January 2012 Volume 1 Issue 3 Kristin Wong, Brendan Liu, Serena McCalla, Benjamin Chu, and Benjamin Hsiao Page 4 of 7 47 remove excess sulfuric acid from the nanofiber surface. After being dried in the oven, the hydrolyzed PAN electrospun membrane was immersed in grafting aqueous solutions (PEI or PVAm) at varied polymer concentrations (2 wt% ~ 10 wt%) for 30 min.. The excessive polymer solution was gently removed from the surface of the membrane with a glass rod, and then the membrane was dried in the oven at 55 °C. Crosslinking of the grafted polymer was applied by immersing the dry grafted nanofibrous PAN membrane into 0.8 wt% Glutaraldehyde (GA) solution for 1 min. then dried at 55 °C. GA ensures that the polymer adheres onto the PAN nanofibers, without dissolving homogeneously in the water, since the polymers are water soluble. The membrane was washed with water and dried in a vacuum oven before heavy metal adsorption tests. Characterization of PVAm/PEI Membrane Fiber Morphology Characterization with SEM: Electrospun membranes were imaged using a scanning electron microscope (SEM) after goldsputter (SC7620 Sputter Coater, Quorum Technologies). The fiber diameter was analyzed from the SEM images using Leica software. SEM images were received from Phenom. Results were reported as mean ± standard deviation. FTIR: Degree of hydrolyzation of PAN membrane in sulfuric acid was characterized using Fourier transform infrared spectroscopy (FTIR) qualitatively. Pore Size Characterization: The mean pore size, the maximum pore size, and the pore size distribution of the nanofibrous membranes were determined by using a capillary flow porometer. A wetting fluid GalwickTM with a surface tension of 15.9 dynes/cm was used to wet the membrane to prevent the disruption of the membrane’s surface properties. Pure Water Flux Test: The pure water flux of the membranes was measured by dead-end filtration at the ambient temperature using Milli Q water. A dead-end filtration cell (Millipore, USA) with an effective filtration area of 3.9 x 10-4 m2 was used for the flux measurements. Heavy Metal Adsorption Test: Dry modified PAN electrospun membrane was weighed (~ 5 mg) and stirred in 20 mL solutions with different initial Cr(VI) concentrations ranging from 5 ug/mL, 10 ug/mL, 20u g/mL, 40 ug/mL to 100 ug/mL. The concentration of the Cr (VI) in solution was determined with UV-Visible Spectroscopy. The amount adsorbed (mg/g) was calculated in Equation 3, q is the amount adsorbed (mg/g), C0 is the initial Cr(VI) concentration, and Cf is the final Cr(VI) adsorption after 24 hours. V is the solution volume, and M is the weight of the PVAm-PAN membrane used. Saturation adsorption capacity of the membrane was calculated according to the Langmuir model, which is given in Equation 4, where Qe is the equilibrium adsorption capacity, Ce is the equilibrium Cr(VI) concentration in solution, Qm is the saturation adsorption capacity, and KL is the adsorption equilibrium constant. The Langmuir model is the most common model used to determine the amount of adsorbate adsorbed on an adsorbent. Equation 3. The concentration of the Cr (VI) adsorbed (mg/g). Equation 4. Saturation adsorption capacity of the membrane. Results Cellulose Nanofiber Membrane Performance Anti-Fouling Performance In order to determine the anti-fouling properties of each membrane, an anti-fouling test was carried out. The water flux of the 0.02% CNF + 0.2% PEGDA membrane (experimental membrane) became constant after 45 minutes, maintaining a flux of approximately 10.1 L/m2 h at 30 psi. The water flux of the 0.02% CNF + 0.2% PEGDA membrane reached a plateau after 45 minutes of testing. This indicates the high anti-fouling performance of the PEGDA membrane. The Koch HFK 328 membrane exhibited the highest initial flux, attributed to its large pore size (5 kDa). The water flux of the Koch membrane become constant after 55 minutes, approximately 20% longer than the time it took for the PEGDA membrane water flux. Due to the large pore size difference of the Pall membranes, the Pall 5K membrane exhibited an initial flux of 45 L/m2 h (at 30 psi), approximately 25 L/m2 h greater than that of the Pall 3K membrane (Figure 3). Rejection and Flux Recovery Performance The rejection ratio was determined in order to evaluate the filtration performance of each membrane. The PEGDA (0.02% CNF + 0.2% PEGDA) membrane exhibited a rejection ratio of 90%, which was higher than that of all commercial membranes tested. The rejection ratio of the Pall 5K membrane was higher than that of the Pall 3K membrane by 9%. Although the Koch 328 membrane exhibited the highest initial flux (Figure 3), its rejection was 35% lower than that of the PEGDA membrane. Concluding from the performance of the MWCO and water permeance, the rejection ratio of the PEGDA membrane was 35%-65% higher than that of the three chosen commercial UF membranes. The higher rejection ratio of PEGDA indicates that the experimental membrane served as a more efficient filter; this can be attributed to the hydrophilic properties of PEGDA and the hydrophobic properties of polyethersulfone (PES) in the Figure 3. Comparison of water flux (at 30 psi) of PEGDA membrane and commercial membranes (Pall 5K, Pall 3K, Koch HFK 328). January 2012 Volume 1 Issue 3 commercial membranes (Figure 4). The recovery ratio was determined by comparing the water flux before and after flushing the membranes with deionized water. The PEGDA (.02% CNF and 0.2% PEGDA) membrane exhibited a recovery ratio of 99%, indicative of a decrease in fouling (Figure 5). Water Contact Angle Test A water contact angle test was performed with the use of an optical contact angle meter (CAM200, KSV Instruments, LTD). The water contact angles of the PEGDA/MBAA and PEGDA membranes were significantly lower than that of the commercial membranes, Koch HFK 328 and Pall 5K, respectively. The PEGDA/MBAA and PEGDA membranes had a higher surface hydrophilicity than the commercial membranes. It is interesting to note that the water droplets placed onto the experimental membranes disappeared within a few seconds, while the water droplets placed onto the commercial membranes remained for 4-5 minutes. This is indicative of the higher surface hydrophilicity of the experimental membranes, meaning that they had better anti-fouling properties than the commercial membranes. The hydrophobicity of the PES integrated in the Koch and Pall membranes caused their surfaces to have higher water contact angles (Figure 6). PVAm/PEI Membrane Performance SEM Images of Polymer-Coated Membrane Figure 7 shows the effect of sulfuric acid on fiber diameter and thickness of the PAN electrospun membrane after being immersed in sulfuric acid. The size of the fiber did not drastically change and was able to maintain minimal size. PAN electrospun nanofibers are non-charged. However, an electrostatic interaction occurred after introducing negative charges onto the surface of the electrospun PAN membrane. Positively charged grafted polymers were able to bind to the PAN electrospun membrane, enhancing the ability of heavy metals to adsorb to the surface of the membrane. Branching of the polymers also increased with the presence of increasing concentrations of sulfuric acid. The rise in polymer branching increased surface area, enhancing heavy metal adsorption. PVAm in solution was initially water soluble, meaning PVAm would not adhere to the membrane when submerged in water. However, with GA crosslinking, PVAm was able to bind and cling to the membrane, making it insoluble in water. Characterization of Functional Groups Many different functional groups were introduced onto the surface of the electrospun membrane after being etched with sulfuric acid. As represented in Figure 8, the –CN and –CH2– functional groups were most abundant after using the highest concentration of the sulfuric acid. PVAm already had a functional group that exhibited heavy metal adsorption, the amine group. The positively charged amine group attracted the Chromium (VI) ions to remove heavy metal from wastewater after being grafted. In Figure 9, a schematic diagram shows the active sites of heavy metal adsorption, amine groups, and the GA crosslinking of the PVAm polymer. Comparison of Heavy Metal Adsorption Rates of Polymer-Coated Membranes The polymer PVAm adsorbed more heavy metal ions when compared to the polymer PEI. PVAm was more efficient because of its pore size, water retention, and strength of the electrically spun fibers. Increasing the polymer concentration also allowed for an increase in Chromium (VI) adsorption rate. With more polymers coated onto the surface of the membrane, more heavy metal ions are able to adsorb onto the surface of the membrane in order for water filtration to occur. Moreover, Kristin Wong, Brendan Liu, Serena McCalla, Benjamin Chu, and Benjamin Hsiao Page 5 of 7 48 Figure 4. Filtration Membrane Rejection Ratio Comparison (feeding solution: PEG 10000) of PEGDA membrane and commercial membranes (Koch HFK 328, Pall 5K, Pall 3K, respectively). Figure 5. Filtration Membrane Recovery Ratio. Comparison of PEGDA membrane and commercial membranes (Koch HFK 328, Pall 5K, Pall 3K, respectively). Figure 6. Water contact angles of PEGDA membrane, PEGDA/MBAA and commercial membranes (Koch HFK 328, Pall 5K). The horizontal line indicates the border between the water droplet and the membrane. Figure 7. SEM images of electrospun nanofiber membranes after being immersed in various sulfuric acid concentrations. January 2012 Volume 1 Issue 3 Discussion A novel cellulose and PEGDA coated membrane was created for filtering water with reduced fouling and increased water permeance. It was found that the membranes coated with PEGDA exhibited the highest rejection and recovery rates, which resulted from the hydrophilic nature of PEGDA. Since the PEGDA membrane had the highest recovery rate, it was least affected by the symptom of fouling. It was also found that the large pore size of the commercial membranes tested, (Pall 3K, Pall 5K, and Koch 328) affected their ultrafiltration performance by decreasing the water flux. The use of electrospun PAN membrane also proved to be effective and efficient when adsorbing Chromium (VI) ion particles. The PVAm membrane adsorbed a greater amount of Chromium (VI) ions from the turbid water than the PEI membrane. Concentration of the polymers, PVAm and PEI, also played an effective role as it directly correlated to the adsorption rates of heavy metals ions. Increasing the concentration of the polymers established numerous amounts of polymers onto the surface of the PAN electrospun membrane for efficient heavy metal removal. With the addition of polymer grafting onto the electrospun membranes, the fiber diameter increased and pore size decreased for increased surface area. This research can also lead to the development of new, foulingresistant, nanofiltration membranes that can help alleviate worldwide water shortages. The membranes incised with sulfuric acid can be used to help industrial wastewater treatment. These charges etched onto the surface of the membrane bonded with the polymers and attracted heavy metal ions in contaminated water because of the existing amine groups of the polymer. The modified membranes efficiently removed heavy metal from wastewater in a short amount of time. the increase in polymer concentration permits an increase in effective areas found on the membrane. Effective areas indicated the amount of heavy metals to be adsorbed onto the surface of the polymer-grafted membrane. Various areas of the membrane have the capability to adsorb heavy metal ions, rather than having only one spot, or certain areas(Table 2). Figure 8. The characterization and functional groups present on the surface of the PAN membrane after being etched with sulfuric acid. Figure 9. Schematic diagram of PVAm polymer with active sites (amine group) and polymer crosslinking. Table 2. Comparison of PAN-PVAm and PAN-PEI nanofiber membrane adsorption rates after being treated varied polymer concentrations. Initial Cr(VI) solution was 10 ug/mL in the adsorption test. Adsorption rate was reported in the result of Cr(VI) amount adsorbed per gram of the whole PVAm-PAN membrane, in which PVAm takes up ~8% in weight. Kristin Wong, Brendan Liu, Serena McCalla, Benjamin Chu, and Benjamin Hsiao Page 6 of 7 49 January 2012 Volume 1 Issue 3 Future InvestigationsIt is necessary to repeat these experiments and investigate theintegration of other hydrophilic polymers into cellulose nanofibermembranes. Furthermore, to determine the fouling resistanceof these membranes, additional testing is required as foulingresistance is critical to the commercial viability of desalinationmembranes. A dually effective filter of waste that reduces foulingand adsorbs heavy metal should also be investigated in the future.If the PAN is removed from the filter and modified, it may causethe filter system to exhibit both beneficial properties when itis restored (anti-fouling and heavy metal adsorption). It is alsocrucial to investigate the results of long-term running experiments(24 hours, 48 hours, etc). Lastly, dynamic adsorption tests shouldbe conducted to determine the membrane’s versatility. Dynamicadsorption tests will provide a different aspect in filtrating heavymetal water as it is pressurized through a syringe pump. Multipleheavy metals, such as lead, copper, and zinc should also be utilizedto help validate the created membrane’s proficiency in removingheavy metal from water. References1.Hanjra, M. A., & Qureshi, M. E. (2010). Global water crisis andfuture food security in an era of climate change. Food Policy, 35, 365-377. 2.Floeri, O., & Coutts, A. (2009). Potential ramifications of the globalnext term economic previous term crisis next term on human-mediateddispersal of marine non-indigenous species. Marine Pollution Bulletin,58, 1595-1598. 3.Gasson, C. (2009). Global water crisis promotes desalination boom.Membrane Technology, 1, 10-11. 4.American Membrane Technology Association (Ed.). (2007,February). Water Desalination Processes, 8. 5.Kar, D., Sur, P., Mandal, S. K., Saha, T., & Kole, R. K. (2008).Assessment of heavy metal pollution in surface water. Int. J. Environ. Sci.Tech., 5, 119-124. 6.Religa, P., Kowalik, A., & Gierycz, P. (2011). Application ofnanofiltration for chromium concentration in the tannery wastewater. Journalof Hazardous Materials, 186(1), 288-292. 7.Kalidhasan, S., & Rajesh, N. (2009). Simple and selective extractionprocess for chromium (VI) in industrial wastewater. Journal of HazardousMaterials, 170(2-3), 1079-1085. 8.Shanker, A. K., & Venkateswarlu, B. (2011). Chromium:Environmental pollution, health effects and mode of action. Encyclopediaof Environmental Health, 650-659.9.Desai, K., Kit, K., Li, J., & Zivanovic, S. (2007). Morphologicaland Surface Properties of Electrospun Chitosan Nanofibers.Biomacromolecules, 2008(9), 1000-1006. 10.Zdyrko, B., Iyer, K. S., & Luzinov, I. (2006). Macromolecularanchoring layers for polymer grafting: comparative study. Polymer, 47(3),272-279.11.Saeed, K., Park, S.-Y., & Oh, T.-J. (2011). Preparation of Hydrazine-Modified Polyacrylonitrile Nanofibers for the Extraction of Metal Ions fromAqueous Media. Journal of Applied Polymer Science, 121, 869-873. 12.Jeon, C., Nah, I. W., & Hwang, K.-Y. (2007). Adsorption of heavymetals using magnetically modified alginic acid. Hydrometallurgy, 86(3-4), 140-146. 13.Ma, H., Burger, C., Hsiao, B. S., & Chu, B. (2011). Ultra-finecellulose nanofibers: new nano-scale materials for water purification. Journalsof Materials Chemistry, 21, 7507-7510. 14.Yung, L., Ma, H., Wang, X., Yoon, K., Wang, R., Hsiao, B. S., &Chu, B. (2010). Fabrication of thin-film nanofibrous composite membranesby interfacial polymerization using ionic liquids as additives. Journal ofMembrane Science, 365, 52-58. 15.Ju, H., McCloskey, B. D., Sagle, A. C., Wu, Y.-H., Kusuma, V.A., & Freeman, B. D. (2008). Crosslinked poly(ethylene oxide) foulingresistant coating materials for oil/separation. Journal of MembraneScience, 307, 260-267. 16.Hahn, M. S., Liao, H., Munoz-Pinto, D., Qu, X., Hou, Y., &Grunlan, M. A. (2008). Influence of hydrogel mechanical propertiesand mesh size on vocal fold fibroblast extracellular matrix production andphenotype. Acta Biomater, 4, 1161-1171. 17.Liu, G., Yang, X., Wang, Y. (2007). Preparation of monodispersehydrophilic polymer microspheres with N,N’-methylenebisacrylamideas crosslinker by distillation precipitation polymerization. PolymerInternational, 56, 905-913. 18.Zou, L., Vidalis, I., Steele, D., Michelmore, A., Low, S., &Verberk, J. (2011). Surface hydrophilic modification of RO membranesby plasma polymerization for low organic fouling. Journal of MembraneScience, 369, 420-428. 19.Charcosset, C. (2006). Membrane processes in biotechnology: Anoverview. Biotechnology Advances, 24, 482-492. 20.Decker, C., Keller, L., Zahoully, K., & Benfarhi, S. (2005).Synthesis of nanocomposite polymers by UV-radiation curing. Polymer,46, 6640-6648. 21.He, G. S., Markowicz, P. P., Lin, T.-C., & Prasad, P. N. (2002).Observation of stimulated emission by direct three-photon excitation.Nature, 767-770. 22.Dai, Z.-W., Wan, L.-S., & Xu, Z.-K. (2008). Surface glycosylationof polyacrylonitrile ultrafiltration membrane to improve its anti-foulingperformance. Journal of Membrane Science, 325, 479-485. AcknowledgementsWe thank Zhe Wang and Yang Liu, Graduate Students, Stony Brook University, for assisting with the collection of data.Kristin Wong, Brendan Liu, Serena McCalla, Benjamin Chu, and Benjamin HsiaoPage 7 of 7 50January 2012 Volume 1 Issue 3